You can add it at the end of structures.xls and then export it to csv. The xls is in the DATA\database directory, I suggest you start copying another national structure, then change the ID (first column) and the rest as you see fit.
AGEOD Team - Makers of Kingdoms, Empires, ACW2, WON, EAW, PON, AJE, RUS, ROP, WIA.